# Microwave Food Trays Reuse
**URL:** https://boards.straightdope.com/t/microwave-food-trays-reuse/735370
**Category:** Factual Questions
**Created:** [October 21, 2015, 5:48pm UTC](https://boards.straightdope.com/t/microwave-food-trays-reuse/735370 "2015-10-21T17:48:38Z")
**Posts on this page:** 4
**Page:** 1
### Author:  [@Broomstick](https://boards.straightdope.com/u/Broomstick)
#### Post date: [October 21, 2015, 5:48pm UTC](https://boards.straightdope.com/t/microwave-food-trays-reuse/735370/1 "2015-10-21T17:48:38Z")
A lot, if not most, trays that comes with microwave food say do not reheat.
Like quite a few people, my household can and does re-use them on occasion.
What’s the deal on this? Is it the food company covering their butts in case some idiot nukes the tray to the point of melting and tries to sue? Or is there actually a real issue there?
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### Author:  [@Ornery\_Bob](https://boards.straightdope.com/u/Ornery_Bob)
#### Post date: [October 21, 2015, 5:59pm UTC](https://boards.straightdope.com/t/microwave-food-trays-reuse/735370/2 "2015-10-21T17:59:19Z")
According to Harvard Medical School:
Microwavable takeout dinner trays are formulated for one-time use only and will say so on the package.
Old, scratched, or cracked containers, or those that have been microwaved many times, may leach out more plasticizers.
The whole article on cooking food in plastic is worth the read, I think. [Microwaving food in plastic: Dangerous or not?](http://www.health.harvard.edu/staying-healthy/microwaving-food-in-plastic-dangerous-or-not)
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### Author:  [@jtur88](https://boards.straightdope.com/u/jtur88)
#### Post date: [October 21, 2015, 7:26pm UTC](https://boards.straightdope.com/t/microwave-food-trays-reuse/735370/3 "2015-10-21T19:26:43Z")
There is no warning on diary product tubs against reusing them to store leftovers, which leads me to believe that the reason for the warning has some association with the microwaving process.
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### Author:  [@Irishman](https://boards.straightdope.com/u/Irishman)
#### Post date: [October 22, 2015, 12:33pm UTC](https://boards.straightdope.com/t/microwave-food-trays-reuse/735370/4 "2015-10-22T12:33:01Z")
Per the link provided by **Ornery Bob** :
> [@](#):
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> Some of these tests measure the migration of chemicals at temperatures that the container or wrap is likely to encounter during ordinary use. For microwave approval, the agency estimates the ratio of plastic surface area to food, how long the container is likely to be in the microwave, how often a person is likely to eat from the container, and how hot the food can be expected to get during microwaving. The scientists also measure the chemicals that leach into food and the extent to which they migrate in different kinds of foods.
The risk appears to be from heating, especially melting. Note: I have melted plastic into my food accidentally, I don’t recommend eating it.
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> Most takeout containers, water bottles, and plastic tubs or jars made to hold margarine, yogurt, whipped topping, and foods such as cream cheese, mayonnaise, and mustard are not microwave-safe.
I have had problems with takeout containers, and now transfer food to reheat.
Side problem - tomato sauce is especially problematic for plastic, especially in a microwave. I don’t know about transfer of chemicals, but if the plastic takes on a permanent orange cast and has surface irregularities, that indicates something going on.
> [@](#):
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> Microwavable takeout dinner trays are formulated for one-time use only and will say so on the package.
This gets back to the calculation factors of duration of use. Also, the companies are required to test to certify the use they expect, so it’s cheaper to state “use only one time” and limit their testing requirements. They don’t have to certify the containers for a 5 year life or 1000 uses or 10,000 minutes or whatever. They limit the time to the duration on the package, likely with a safety factor for time, temps, etc.
The containers themselves may be safe for repeated use, but they aren’t tested and certified for that.